This invention relates to novel multiple gas discharge display/memory panels or units which have an electrical memory and which are capable of producing a visual display or representation of data such as numerals, letters, television display, radar displays, binary words, etc.
Multiple gas discharge display and/or memory panels of one particular type with which the present invention is concerned are characteristized by an ionizable gaseous medium, usually a mixture of at least two gases at an appropriate gas pressure, in a thin gas chamber or space between a pair of opposite dielectric charge storage members which are backed by conductor (electrode) members, the conductor members backing each dielectric member typically being transversely oriented to define a plurality of discrete gas discharge units or cells.
In some prior art panels the discharge units are additionally defined by surrounding or confining physical structure such as by cells or apertures in perforated glass plates and the like so as to be physically isolated relative to other units. In either case, with or without the confining physical structure, charges (electrons, ions) produced upon ionization of the elemental gas volume of a selected discharge unit, when proper alternating operating potentials are applied to selected conductors thereof, are collected upon the surfaces of the dielectric at specifically defined locations and constitute an electrical field opposing the electrical field which created the so as to terminate the discharge for the remainder of the half cycle and aid in the initiation of a discharge on a succeeding opposite half cycle of applied voltage, such charges as are stored constituting an electrical memory.
Thus, the dielectric layers prevent the passage of substantial conductive current from the conductor members to the gaseous medium and also serve as collecting surfaces for ionized gaseous medium charges (electrons, ions) during the alternate half cycles of the A.C. operating potentials, such charges collecting first on one elemental or discrete dielectric surface area and then on an opposing elemental or discrete dielectric surface area on alternate half cycles to constitute an electrical memory.
An example of a panel structure containing non-physically isolated or open discharge units is disclosed in U.S. Pat. No. 3,499,167 issued to Theodore C. Baker, et al.
An example of a panel containing physically isolated units is disclosed in the article by D. L. Bitzer and H. G. Slottow entitled "The Plasma Display Panel -- A Digitally Addressable Display With Inherent Memory", Proceeding of the Fall Joint Computer Conference, IEEE, San Francisco, California, Nov. 1966, pages 541-547. Also reference is made to U.S. Pat. No. 3,559,190.
In the construction of the panel, a continuous volume of ionizable gas is confined between a pair of dielectric surfaces backed by conductor arrays forming matrix elements. The cross conductor arrays may be orthogonally related (but any other configuration of conductor arrays may be used) to define a plurality of opposed pairs of charge storage areas on the surfaces of the dielectric bounding or confining the gas. Thus, for a conductor matrix having H rows and C columns the number of elemental discharge units will be the product H .times. C and the number of elemental or discrete areas will be twice the number of such elemental discharge units.
In addition, the panel may comprise a so-called monolithic structure in which the conductor arrays are created on a single substrate and wherein two or more arrays are separated from each other and from the gaseous medium by at least one insulating member. In such a device the gas discharge takes place not between two opposing electrodes, but between two contiguous or adjacent electrodes on the same substrate; the gas being confined between the substrate and an outer retaining wall.
It is also feasible to have a gas discharge device wherein some of the conductive or electrode members are in direct contact with the gaseous medium and the remaining electrode members are appropriately insulated from such gas, i.e., at least one insulated electrode.
In addition to the matrix configuration, the conductor arrays may be shaped otherwise. Accordingly, while the preferred conductor arrangement is of the crossed grid type as discussed herein, it is likewise apparent that where a maximal variety of two dimensional display patterns is not necessary, as where specific standardized visual shapes (e.g., numerals, letters, words, etc.) are to be formed and image resolution is not critical, the conductors may be shaped accordingly, i.e., a segmented display.
The gas is one which produces visible light or invisible radiation which stimulates a phosphor (if visual display is an objective) and a copious supply of charges (ions and electrons) during discharge.
In prior art, a wide variety of gases and gas mixtures have been utilized as the gaseous medium in a gas discharge device. Typical of such gases include CO; CO.sub.2 ; halogens, nitrogen NH.sub.3 ; oxygen; water vapor; hydrogen; hydrocarbons; P.sub.2 O.sub.5 ; boron fluoride; acid fumes; TiCl.sub.4 ; Group VIII gases; air; H.sub.2 O.sub.2 ; vapors of sodium, mercury, thallium, cadmium, rubidium, and cesium; carbon disulfide; laughing gas; H.sub.2 S; deoxygenated air; phosphorus vapors; C.sub.2 H.sub.2 ; CH.sub.4 ; naphthalene vapor; anthracene; Freon, ethyl alcohol; methylene bromide; heavy hydrogen; electron attaching gases; sulfur hexafluoride; tritium; radioactive gases; and the rare or inert gases.
In one preferred practice hereof, the gas mixture comprises at least one rare gas, more preferably at least two rare gases, selected from neon, argon, xenon, krypton and radon. Beneficial amounts of mercury and/or helium may also be present.
In an open cell Baker, et al. type panel, the gas pressure and the electric field are sufficient to laterally confine charges generated on discharge within elemental or discrete dielectric areas within the perimeter of such areas, especially in a panel containing non-isolated units.
As described in the Baker, et al. patent, the space between the dielectric surfaces occupied by the gas is such as to permit photons generated on discharge in a selected discrete or elemental volume of gas to pass freely through the gas space and strike surface areas of dielectric remote from the selected discrete volumes, such remote, photon struck dielectric surface areas thereby emitting electrons so as to condition at least one elemental volume other than the elemental volume in which the photons originated. To condition an elemental volume is to provide at least one free electron therein.
With respect to the memory function of a given discharge panel, the allowable distance or spacing between the dielectric surfaces depends, inter alia, on the frequency of the alternating current supply, the distance typically being greater for lower frequencies.
While the prior art does disclose gaseous discharge devices having externally positioned electrodes for initiating a gaseous discharge, sometimes called "electrodeless discharge", such prior art devices utilized frequencies and spacings or discharge volumes and operating pressures such that although discharges are initiated in the gaseous medium, such discharges are ineffective or not utilized for charge generation and storage at higher frequencies; although charge storage may be realized at lower frequencies, such charge storage has not been utilized in a display/memory device in the manner of the Bitzer-Slottow or Baker, et al. invention.
The term "memory margin" is defined herein as EQU M. M. = (V.sub.f -V.sub.E)/V.sub.f /2)
where V.sub.f is the half amplitude of the smallest sustaining voltage signal which results in a discharge every half cycle, but at which the cell is not bi-stable and V.sub.E is the half amplitude of the minimum applied voltage sufficient to sustain discharges once initiated.
It will be understood that the basic electrical phenomenon utilized in this invention is the generation of charges (ions and electrons) alternately storable at pairs of opposed or facing discrete points or areas on a pair of dielectric surfaces backed by conductors connected to a source of operating potential. Such stored charges result in an electrical field opposing the field produced by the applied potential that created them and hence operate to terminate ionization in the elemental gas volume between opposed or facing discrete points or areas of dielectric surface. The term "sustain a discharge" means producing a sequence of momentary discharges, one discharge for each half cycle of applied alternating sustaining voltage, once the elemental gas volume has been fired, to maintain alternate storing of charges at pairs of opposed discrete areas on the dielectric surfaces.
In accordance with the practice of this invention, there is incorporated into the dielectric of a gas discharge device a beneficial amount of a source of at least one element selected from selenium, tellurium, and polonium.
As used herein, the phrase "incorporated into" is intended to comprise any suitable means whereby a source of the selected element is appropriately combined with the dielectric, such as by intimately adding or mixing the source into the dielectric premelt batch or to the melt; by ion exchange; by ion implantation; by diffusion techniques; or by applying one or more layers to the charge storage surface of the dielectric, or to the electrode contact surface of the dielectric, or as an internal layer within the dielectric.
In one particular embodiment hereof, the source of the selected element is applied as one or more layers to the charge-storage surface of the dielectric.
As used herein, the term "layer" is intended to be all inclusive of other similar terms such as film, deposit, coating, finish, spread, covering, etc.
It is contemplated that the element source may be applied as a layer over one or more previously applied dielectric layers. Likewise, one or more layers of other substances may be applied over the layer of the element source. Such other dielectric layers may comprise luminescent phosphors and/or any other suitable compounds, especially inorganic compounds of Al, Pb, Si, Ti Hf, rare earths (e.g., thorium), Group IA (e.g., cesium), and/or Group IIA (e.g., magnesium).
The source of the selected element is applied to the dielectric surface (or over a previously applied layer) by any convenient means including not by way of limitation vapor deposition; vacuum deposition; chemical vapor deposition; wet spraying upon the surface a mixture of solution of the layer substance suspended or dissolved in a liquid followed by evaporation of the liquid; dry spraying of the layer upon the surface; thermal evaporation using direct heat, electron beam, or laser; plasma flame and/or arc spraying and/or deposition; and sputtering target techniques.
Each layer of the source of selenium, tellurium, and polonium is applied to the dielectric, as a surface or sub-layer, in an amount sufficient to obtain the desired beneficial result, usually to a thickness of at least about 100 angstrom units, usually within a range of about 200 angstrom units per layer up to about 1 micron (10,000 angstrom units) per layer.
In the fabrication of a gaseous discharge panel, the dielectric material is typically applied to and cured on the surface of a supporting glass substrate or base to which the electrode or conductor elements have been previously applied. The glass substrate may be of any suitable composition such as a soda lime glass composition. Two glass substrates containing electrodes and cured dielectric are then appropriately sealed together, e.g., using thermal means, so as to form a panel.
In one preferred practice of this invention, each element containing layer is applied to the surface of the cured dielectric before the panel heat sealing cycle, with the substrate temperature during the layer application ranging from about 150.degree. F. to about 600.degree. F.
In the practice of this invention it is contemplated using any suitable source of selenium, tellurium, or polonium, especially inorganic compounds.
Although insulating or semi-conductor materials are typically used, conductor materials may be used if the material is appropriately isolated within or on the dielectric so as not to be in conductive electrical contact with a source of potential and/or ground.
Likewise if a conductive material is used in a multiple cell device, the geometric arrangement of the material may be such that no two cells are electrically connected by the conductive material. For example, a conductive material could be deposited as a spot over each discharge site. Likewise, nonconductive materials (as well as the elements) can be deposited as spots.
The selected source is typically a solid. However, liquid materials may be used, especially if applied in a suitable binder.
Typical inorganic selenium compounds include selenium monobromide, selenium tetrabromide, selenium monobromide trichloride, selenium bibromide chloride, selenium monochloride, selenium tetrachloride, seleneium hexafluoride, selenium tetrafluoride, selenium monoiodide, senlenium tetraiodide, selenium carbide, selenium hydride, selenium nitride, selenium dioxide, selenium trioxide, selenium oxybromide, selenium oxychloride, selenium oxyfluoride, selenium sulfur oxytetra chloride, selenium disulfide, selenium monosulfide, and selenium sulfur oxide.
Typical inorganic tellurium compounds include tellurium dibromide, tellurium tetrabromide, tellurium dichloride, tellurium tetrachloride, tellurium hexafluoride, tellurium tetrafluoride, tellurium hydride, tellurium diiodide, tellurium tetraiodide, tellurium dioxide, tellurium monoxide, tellurium trioxide, tellurium sulfide, and tellurium sulfoxide.
Typical inorganic polonium compounds include polonium monobromide, polonium tribromide, polonium tetrabromide, polonium monochloride, polonium trichloride, polonium tetrachloride, polonium monoiodide, polonium trichloride, polonium monofluoride, polonium trifluoride, polonium tetrafluoride; polonium dioxide, polonium selenate, polonium basic sulfate, polonium disulfate, and polonium monosulfide.
In addition, the selenium, tellurium, or polonium may be used in elemental form, such as distributed throughout the dielectric or applied continuously or discontinuously to the dielectric surface.
The use of this invention has many potential benefits. For example, sources of the selected element may be used alone or in combination with the other elements (such as enumerated hereinbefore) to achieve lower panel operating voltages, thermal stability, more uniform panel operating voltages, decreased aging cycle time, etc.
In the practice of this invention, it is contemplated that the source of selenium, tellurium, and polonium may contain one or more of such elements. Likewise, it is especially contemplated using intermetallic compounds containing one or more of the elements in combination with one or more other metals such as nickel selenide. Likewise, salts of other metals may be utilized, e.g., nickel selenate. This may be particularly beneficial where multiple materials are being applied to the dielectric to achieve a given result.